Polyesters such as poly(ethylene terephthalate) (PET) are widely used in bottles and containers for carbonated beverages, fruit juices, and certain foods. Because of the limited barrier properties of polyesters with regard to oxygen and other gases, polyester nanocomposites have been developed which contain chemically modified organoclay materials. Due to the high aspect ratio of the organoclays selected for the formation of polyester nanocomposites, frequently a tortuous path is created which the penetrating gas must follow to diffuse through this material, thus markedly increasing the barrier of the polyester material.
One of the primary processes which has been used to form bottles and containers from polyester nanocomposites is stretch blow molding (SBM). With this blow molding process, usually the preform is molded at a temperature about 20 to 50 degrees Celsius above the glass transition temperature of the polyester. Molding in this range of temperature, it has been very difficult to form a bottle or container which did not exhibit substantial opacity or cloudiness in the sidewall. It is very desirable to have processing methods available which allow the formation of polyester nanocomposite containers possessing both high clarity and barrier.
There are many examples in the patent literature of the formation of polymer/clay nanocomposites containing, for example, Nylon-6 and alkyl ammonium treated montmorillonite. Some patents describe the blending of up to 60 weight percent of intercalated clay materials with a wide range of polymers including polyamides, polyesters, polyurethanes, polycarbonates, polyolefins, vinyl polymers, thermosetting resins and the like. WO 93/04117 discloses a wide range of polymers melt blended with up to 60 weight percent of dispersed platelet particles. Although the use of polyesters is disclosed, polyester/platelet compositions of a specific molecular weight are not disclosed. WO 93/04118 discloses composite material of a melt processable polymer and up to 60 weight percent of dispersed platelet particles. Among a wide range of thermoplastic polymers indicated, polyesters are included. U.S. Pat. No. 5,552,469 describes the preparation of intercalates derived from certain clays and water soluble polymers such as polyvinyl pyrrolidone, polyvinyl alcohol, and polyacrylic acid. The specification describes a wide range of thermoplastic resins including polyesters and rubbers which can be used in blends with these intercalates. U.S. Pat. No. 4,889,885 describes the polymerization of various vinyl monomers such as methyl methacrylate and isoprene in the presence of sodium montmorillonite. In Example 11, it describes the polycondensation of dimethyl terephthalate and ethylene glycol in the presence of 33 weight percent of a montmorillonite clay in water (for 6.2 final weight percent of clay in the polyester resin).
JP Kokai patent no. 9-176461 discloses polyester bottles wherein the polyester contains swellable laminar silicate. WO 97/31057 discloses polymer composite having dispersed therein inorganic material such as clay which is separated with an inorganic intercalant. WO 97/31973 discloses producing a composite material by mixing a potassium ionomer in which ethylene methacrylate copolymer is either partially or completely neutralized with an organic polymer. However, the foregoing references produce materials comprising very large tactoids and little if any dispersion of individual platelet particles. Nor do any of the references disclose nanocomposite compositions having other specific properties such as melt strength and viscoity and high I.V. which are necessary to produce containers by any method.
For the formation of molded articles from polyester nanocomposites, little specific prior art was found to be in existence. In U.S. Pat. No. 5,102,948, a polyamide/clay composite was formulated in such a manner that the material was resistant to whitening during stretching. With polyester resins, no such prior art has been found.
As an initial attempt to process polyester based nanocomposites, variations of conventional techniques for polyester processing have been utilized in our laboratory to form the objects desired. For blow molding polyester resins into bottles, jars and other containers, several processes are well established: SBM, extrusion blow molding (EBM), and injection blow molding (IBM). Polyester/clay nanocomposites contain dispersed clay particles which frequently also act as nucleation agents for the polyester material. Using SBM to mold bottles of polyester/clay composites frequently imparts sufficient orientation to the wall of the bottle to prevent creep when the contents of the bottle is under pressure. However, initial attempts to employ SBM with these materials consistently yielded bottles which exhibited a hazy or turbid sidewall. Only when high melt strength polyester/clay composite resins were prepared which were processable at high melt temperatures, have containers with clear sidewalls been obtained from these materials.
FIG. 1 is a plot showing the melt viscosity at 280xc2x0 C. as a function of I.V. for polyester-platelet composites and polyesters without any platelet particles.
FIG. 2 is a plot showing the melt strength as a function of I.V. for polyester-platelet composites and polyesters without any platelet particles.